Defining the Active Faults and the associated Geotechnical Properties using MASW Technique in Dehradun district and its Adjoining Regions, India

Abstract

ABSTRACT Dehradun lies in the intermontane Dun Valley in the Garhwal Sub Himalaya, which lies with the Main Boundary Thrust (MBT)- Himalayan Frontal Thrust (HFT) tectonic wedge with other intrawedge faults. These faults may rupture during a great earthquake and cause damage to the existing civil structures in the fault zone. Therefore, it is essential to characterise the active faults in and around Dehradun. We carried out 2D Shear wave velocity profiles across the Markanda Thrust, Rajban Fault, Bata Fault, Santaurgarh Thrust, Bhauwala Thrust, and Majhaun Fault at 18 sites using the Multichannel Analysis of Surface Wave (MASW) technique. The obtained shear wave velocity is further utilised to calculate geotechnical parameters like the average shear wave velocity (Vs30), soil stiffness, amplification factor, and predominant frequency. The weak, weathered or shear zones and dislocations are mapped in terms of a low shear wave velocity layer overlain by a high shear wave velocity layer at deeper depths near identified fault or thrust locations. The active fault/thrust zones in the Dun Valley have a shear wave velocity of 130 m/s to <1500m/s and consist of stiff soil to dense soils of class D to C as per the National Earthquake Hazard Reduction Programme (NEHRP) classification. This study contributes to a better understanding of the seismic characteristics of Dehradun and its surroundings, which is useful for earthquake mitigation studies.